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SNAPSHOT
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On April 3, 1965 a SNAP 10 A nuclear power
system was launched into a 1300-km orbit
with a cesium ion engine as a secondary
payload. The ion beam power supply was
operated at 4500 V and 80 mA to produce a
thrust of about 8.5 mN. The neutralizer was
a barium-oxide-coated wire filament. The ion
engine was to be operated off batteries for
about one hour, and then the batteries were
to be charged for approximately 15 hours
using 0.1 kW of the nominal 0.5 kW SNAP
system as the power supply. The SNAP power
system operated successfully for about 43
days, but the ion engine operated for a
period of less than 1 hour before being
commanded off permanently. Analysis of
flight data indicated a significant number
of high-voltage breakdowns, and this
apparently caused sufficient EMI to induce
false horizon sensor signals leading to
severe attitude perturbations of the
spacecraft. Ground tests indicated that the
engine arcing produced conducted and
radiated EMI significantly above design
levels. It was concluded that low frequency,
< 1 MHz, conducted EMI caused the slewing
of the spacecraft.
The preceding was an excerpt from:
Sovey, J. S., Rawlin, V. K., and Patterson,
M. J.: "Ion Propulsion Development
Projects in U. S.: Space Electric Rocket
Test 1 to Deep Space 1." Journal of
Propulsion and Power, Vol. 17, No. 3,
May-June 2001, pp. 517-526.
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